It remains real because no one can prove it is fake. Exactly what you would expect from an image that is most likely the face of Jesus Christ.

Exodus 20:1-5 God spoke, and these were his words: "Worship no god but me.... Do not bow down to any idol or worship it...

If the shroud really is Jesus' burial cloth and his image was left on it when he was resurrected, that is really great. But remember the second commandment. Even though Catholics say they venerate and don't worship idols, it is the same thing, kissing an icon or idol or praying in front of it, is putting it in the place of God. Focus on God, not his creation.